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Digitech TSR24S

Dual Channel Multi-effects Processor By Derek Johnson & Debbie Poyser
Published October 1995

The trouble with sequels is that they're not usually as good as the originals. Is the follow‑up to Digitech's powerful TSR24 the exception to the rule? Derek Johnson & Debbie Poyser find out.

When affordable digital reverb first started to appear, the average musician was so elated at being able to chuck away his Great British Spring that he was perfectly happy to spend hundreds of pounds on units offering the luxury of 10 or so presets — which could be used any way at all, as long as it was one at a time. These days, though, manufacturers have a rather tougher time persuading us to part with our money: good quality reverb we take for granted; exotic guitar and vocal treatments we expect; ever‑lengthening chains of digital effects no longer surprise us. Being less able to offer revolution, manufacturers now tempt us with evolution — units which provide more features and facilities for less money.

This brings us to the Digitech TSR24S Dual Channel Digital Processor, an upgraded version of the 1993‑vintage TSR24. The original machine justified its £899 price tag with true stereo operation, custom effects algorithm creation, 18‑bit A/D and D/A converters, sampling, two sets of stereo outputs, comprehensive MIDI control, and the fact that it could be used as two discrete stereo processors. In the grand technological tradition of more‑for‑less, the 'S' version reviewed here retains all this power and adds even more, for £100 less than the original TSR24: balanced audio connections, a handful of new mega‑reverbs, chromatic tuner, so‑called 'Whammy' pitch‑bending, stereo gated reverb, mono and stereo modulated delays, 4‑way auto‑panner, single and dual phaser, notch and band‑pass filters, graphic module linking, enhanced mixer modules, and lastly (and perhaps most significantly) PPC200 parallel processor card 'readiness' — at £250, this card effectively doubles your DSP power, allowing twice as many effects to be used at once, adding new algorithms and programs, and doubling sample and delay times. While this is undoubtedly a great feature in itself, what's more exciting is the potential for future enhancements, since Digitech could theoretically make new developments available to TSR24S owners on new cards.

Hold The Front Panel!

Physically, the TSR24S is solidly built, which bodes well for live work, and looks very similar to the original TSR24, the only real front panel difference between old and new being that the majority of the S's buttons are green rather than blue. The TSR24S's large number of buttons, divided into six sections, make for a busy front panel, but in practice allow you to move around the operating system more easily. The six sections are as follows:

  • Global: utility functions such as LCD contrast, MIDI maps, chromatic tuner and footswitch setups; this section also includes a bypass button. Though not labelled 'Global' on the unit, the TSR's manual refers to this group as such.
  • Edit: six buttons used in the creation of custom algorithms.
  • FX Modules: when editing, these buttons take you immediately to the parameters of the effect you've selected. With so many effects available, this is an invaluable facility for speedy editing.
  • Parameter: a cross‑shaped selection of four buttons that scroll through the editable parameters in a program and allow you to change their values.
  • Program: another 4‑button cross used to select programs, store new programs, and compare between edited and original versions.
  • Access: essentially programmable function keys, and you define what they do; for example, you could use them to jump to the parameters you most frequently tweak in a particular program.

All that remains is the data entry knob, the dual input and output level controls, liquid crystal display, LED patch number display, and a variety of status LEDs which indicate MIDI activity, bypass, overload and so on.

Inside Story

The highest level of the TSR24S's operating system is the Program — despite what the manual says, the TSR24S has 128 editable and 112 preset Programs (the manual claims 256 of each), organised in one bank of 240 Programs. You can freely overwrite Programs 1‑128; 129‑240 are preset. Note that Programs 113‑128 are bypassed unless you have the optional PPC200 installed; these show off the capabilities of a double processor‑equipped TSR24S. If you have the standard unit only, you can't use them, but you can overwrite them.

At the heart of each Program is an Algorithm, a configuration of effects. You can select from 24 factory algorithms, or create up to 32 custom algorithms — sound quality aside, this is the single most attractive and powerful feature of the TSR24S. When creating an algorithm from scratch, you have a choice of 78 effects modules, linkable in any order, and 25 mixer modules: mixer modules (which offer up to 16 inputs and a choice of mono, stereo, and 3‑output operation) are needed to patch the effects together. The list of possible effects modules is comprehensive: 10 reverbs, 17 delays, 10 EQs, three samplers, eight choruses and flangers, 10 pitch‑shifters, noise reduction, phasers, tremolos, wah‑wahs and duckers; there's even a phase invertor and tuning reference.

There are restrictions, however. Effect and mixer modules each use up a certain number of CPU and RAM blocks (in Digitech parlance) and you will eventually run out of both. Some effects use a lot of processing while needing little RAM (the EQ and mixer modules fall into this group), while others require lots of RAM (sampling, reverb and delays, for example), so keep these points in mind while planning an algorithm. A total of 228 CPU blocks and 256 RAM blocks are available, and a chart in the manual lists values for every module. As an example, GigaVerb+ (the most powerful reverb module) uses 228 RAM blocks and 220 CPU blocks, which barely leaves room for a bit of EQ or noise reduction and a mixer module. Don't worry, though — there is an efficient reverb module (MFX Reverb) that uses just 30 RAM blocks and 69 CPU blocks. You'll seldom find yourself able to use more than four or five modules in an algorithm, but the total flexibility in patching them together makes up for this apparent failing.

Surfing The System

Programming the TSR24S is, in spite of the manual, relatively simple. The FX module buttons allow you to fly around the system without getting too confused; choose your effect, scroll to a parameter, tweak it, have a listen, and save the result. Simple.

As for algorithm creation, Digitech make this easy as well. Firstly, it pays to offline a little work to pen and paper — plan your algorithm, add up the CPU and RAM blocks you'll need, and then go to the TSR24S. Select any algorithm, and press the Add button. This gives you the option to modify a factory algorithm or create one from scratch. Scroll through the modules and press Enter when you reach one you wish to use. When you've made your selections (or run out of Blocks), you patch the effects together. An auto‑link function 'plugs' the modules together in the most logical manner, but manually linking modules, with the aid of the excellent new graphic module linking feature, is simply a matter of scrolling through options and confirming your choice. It works like a small‑screen version of Apple's MIDI Manager for Macintosh computers.

One of the most attractive selling points of the TSR24S is its ability to be used as two discrete processors. The biggest compromise is that your total of four or five effects modules per algorithm is now split in two. There are three factory 2‑channel algorithms, but you can also programme your own; it's possible to create some excellent everyday effects for both channels, but off‑the‑wall processing is best left to single chains — or to a PPC200‑equipped TSR24S, which effectively means two TSR24Ss in one box. Hmmm, that card option is beginning to look attractive...

Digitech's S‑DISC based processors produce some of the cleanest, most complex reverbs available in affordable packages.

One other easily overlooked feature that saves money is the built‑in chromatic tuner, accessible under the Utility button. This is blissfully easy to use, not to mention accurate. You simply alter an instrument's tuning until the strobing vertical bars at the bottom of the LCD stop moving — the tuner automatically detects which note you're trying to tune. The overall tuning reference can be altered between A = 427 and 453, or set to A‑flat, G or G‑flat, so if you want to tune to a lower, renaissance reference point, this is the machine for you.

Sadly, the TSR24S's manual is not very intuitive, and contains several confusing inaccuracies. For example, the algorithm list gives details of all 32 factory algorithms, which includes several algorithms (27‑32, says the manual) not available unless you've got the PPC200 installed. However, the number of algorithms on the unexpanded review model is just 24. So where are algorithms 25 and 26?

FX (Almost) Unlimited

It's been said before, but Digitech's S‑DISC based (Static/Dynamic Instruction Set Computer) processors produce some of the cleanest, most complex reverbs available in affordable packages. The TSR24S is no exception: its reverbs offer programmability unavailable at this price elsewhere — as an example, the completely OTT ExaVerb preset has an astonishing 28 editable parameters intended to allow you to convincingly recreate acoustic spaces. The reverbs tend to be bright, but not in the metallic way of some Japanese processors, offering clarity and realism instead. The rest of the effects are equally excellent: delays and samples (up to 5 seconds mono; 2.5 seconds stereo) provide subjectively perfect replications of the input signal; choruses and flangers are rich and exciting (perfect for guitar processing); and the EQ modules add a good deal of creative potential.

Noise performance is good, and the NR modules help where the nature of the effect adds unwanted noise. We thought the pitch‑shifting modules not quite up to the quality offered by the rest of the effects, which is surprising given Digitech's success with their Vocalist range of harmony processors. Even the Whammy‑based effects — derived from the famed digital dive‑bomb control found on certain Digitech guitar products — are a little lumpy. However, while we wouldn't use the modules as serious harmony or pitch correction tools — the delays involved and metallic quality are far too obvious — they can be used effectively for guitar processing or sound effects.

On Reflection...

As a creative tool for the adventurous, the TSR24S scores high. But its complexity and flexibility isn't achieved at the expense of clarity and logic in the operating system, which should be usable even by relative novices. Creating your own algorithms is an incredibly useful facility, is great fun, and can produce some exciting results; it's a shame that the presets don't fully show how exciting a machine this can be in the hands of a reasonably competent programmer (though Presets 4 'Fantasia Guitar', 5 'Icy Cavern', and 86 'Chorus‑8v Med' are notable exceptions). Sound quality is of a high standard, and the character of the TSR's effects is appealing, with enough parameter tweakability to satisfy almost anyone. Expandability via the PPC200 should also help to ensure that the TSR24S stays current and exciting — £250 effectively gives you the processing power of another TSR24S. In short, there's not much wrong with this unit, and the enhancements over the original, coupled with the new lower selling price, mean that it's now an even better buy as an all‑round studio workhorse.

Real‑Time MIDI Control

As befits a hi‑tech product released in 1995, the TSR24S offers comprehensive real‑time MIDI control. Any Continuous Controller can be linked to any TSR24S parameter; up to 10 Local and 20 Global Controller links are possible. Local links are specific to a particular Program, while Global links are always active — if you assign mod wheel to flanger depth, for instance, that link will work in any program that uses the flanger.

To make the link between Controller and parameter, select a parameter, press the MIDI button, and the link is made. Now choose which Controller will do the controlling, its operating range, and that's it.

There are one or two anomalies to watch out for. First of all, you can't hear a particular Controller working unless you exit from the MIDI Utility page — awkward. This situation is exacerbated by the lack of a list of Controllers in the manual. If you want to assign mod wheel or foot controller, for example, you'll need to know that they're actually Controller numbers 2 and 4 respectively — and you'll have to look it up elsewhere! Also, while Local CCs are numbered on the TSR24's display (1 to 10), Global CCs are not, so while you're assigning them, you can lose count of how many you have left.

Apart from some expected parameters exhibiting the 'zipper' effect if altered too quickly (reverb room size, for example), the links work perfectly and add enormously to the creative potential of the unit. Want to gradually lengthen a reverb decay on a fade, or change chorus depth during a track? It's easy with control change linking.

Other MIDI tricks include a Program Change map, SysEx dumping of memory contents, and a MIDI Merge facility that merges data appearing at the MIDI In port with TSR24S data to the MIDI Out.

TSR24S Specification

  • A/D converter: 18‑bit, 128x oversampling delta sigma.
  • D/A converter: 18‑bit PCM.
  • Sampling frequency: 48kHz.
  • Digital signal path: 24‑bit.
  • Internal data path: 48‑bit.
  • Input: 4 quarter‑inch balanced jacks.
  • Output: 4 quarter‑inch balanced jacks.
  • Frequency response: 20Hz‑20kHz.
  • Signal‑to‑noise ratio: 90dB.
  • Factory memories: 24 algorithms, 112 programs.
  • User memories: 32 algorithms, 128 programs.
  • FX groups: Reverb, Delay, Chorus, Pitch, Sample, EQ, Flange, Mod, More (noise gates, silencers, duckers, wahs, phase inverter), Mix.


  • TSR24 review (SOS December 1993).
  • TSR12 review (SOS November 1994).
  • Also coming soon is the TSR6, offering true stereo S‑DISC processing, 99 user and 99 preset memories, and a collection of useful basic algorithms at £299.


  • Effectively two processors in one.
  • Sophisticated and clean sound.
  • Easy custom algorithm creation.
  • Expandable with optional parallel processing card.
  • Efficient chromatic tuner.


  • Can't audition MIDI Controller links while making them.
  • Unhelpful manual.
  • Would be nice to see a better way of installing the PPC200 than taking the lid off the unit — which, by the way, is a bit of a maul.


Recommended for more serious project studio owners looking for an effects unit with a decent shelf‑life, which rewards programming effort. Its ability to be used as two separate processors makes it good value for money, and it could easily be the main or only processor in a small studio.